﻿//
// RtfDecompressor.cs
//
// Author: Kees van Spelde <sicos2002@hotmail.com>
//
// Copyright (c) 2013-2018 Magic-Sessions. (www.magic-sessions.com)
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NON INFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.
//

using System;
using System.Collections.Generic;
using System.Text;

namespace MsgReader.Outlook
{
    /// <summary>
    /// Class used to decompres compressed RTF
    /// </summary>
    internal static class RtfDecompressor
    {
        #region Consts
        private const string Prebuf =
            "{\\rtf1\\ansi\\mac\\deff0\\deftab720{\\fonttbl;}" +
            "{\\f0\\fnil \\froman \\fswiss \\fmodern \\fscript " +
            "\\fdecor MS Sans SerifSymbolArialTimes New RomanCourier" + "{\\colortbl\\red0\\green0\\blue0\n\r\\par " +
            "\\pard\\plain\\f0\\fs20\\b\\i\\u\\tab\\tx";
        #endregion

        #region Fields
        /// <summary>
        /// Contains the prebuf string
        /// </summary>
        private static byte[] _compressedRtfPrebuf;
        #endregion

        #region Crc32Table
        /// <summary>
        /// The lookup table used in the CRC32 calculation
        /// </summary>
        private static readonly uint[] Crc32Table =
                {
                    0x00000000, 0x77073096, 0xEE0E612C, 0x990951BA, 0x076DC419,
                    0x706AF48F, 0xE963A535, 0x9E6495A3, 0x0EDB8832, 0x79DCB8A4,
                    0xE0D5E91E, 0x97D2D988, 0x09B64C2B, 0x7EB17CBD, 0xE7B82D07,
                    0x90BF1D91, 0x1DB71064, 0x6AB020F2, 0xF3B97148, 0x84BE41DE,
                    0x1ADAD47D, 0x6DDDE4EB, 0xF4D4B551, 0x83D385C7, 0x136C9856,
                    0x646BA8C0, 0xFD62F97A, 0x8A65C9EC, 0x14015C4F, 0x63066CD9,
                    0xFA0F3D63, 0x8D080DF5, 0x3B6E20C8, 0x4C69105E, 0xD56041E4,
                    0xA2677172, 0x3C03E4D1, 0x4B04D447, 0xD20D85FD, 0xA50AB56B,
                    0x35B5A8FA, 0x42B2986C, 0xDBBBC9D6, 0xACBCF940, 0x32D86CE3,
                    0x45DF5C75, 0xDCD60DCF, 0xABD13D59, 0x26D930AC, 0x51DE003A,
                    0xC8D75180, 0xBFD06116, 0x21B4F4B5, 0x56B3C423, 0xCFBA9599,
                    0xB8BDA50F, 0x2802B89E, 0x5F058808, 0xC60CD9B2, 0xB10BE924,
                    0x2F6F7C87, 0x58684C11, 0xC1611DAB, 0xB6662D3D, 0x76DC4190,
                    0x01DB7106, 0x98D220BC, 0xEFD5102A, 0x71B18589, 0x06B6B51F,
                    0x9FBFE4A5, 0xE8B8D433, 0x7807C9A2, 0x0F00F934, 0x9609A88E,
                    0xE10E9818, 0x7F6A0DBB, 0x086D3D2D, 0x91646C97, 0xE6635C01,
                    0x6B6B51F4, 0x1C6C6162, 0x856530D8, 0xF262004E, 0x6C0695ED,
                    0x1B01A57B, 0x8208F4C1, 0xF50FC457, 0x65B0D9C6, 0x12B7E950,
                    0x8BBEB8EA, 0xFCB9887C, 0x62DD1DDF, 0x15DA2D49, 0x8CD37CF3,
                    0xFBD44C65, 0x4DB26158, 0x3AB551CE, 0xA3BC0074, 0xD4BB30E2,
                    0x4ADFA541, 0x3DD895D7, 0xA4D1C46D, 0xD3D6F4FB, 0x4369E96A,
                    0x346ED9FC, 0xAD678846, 0xDA60B8D0, 0x44042D73, 0x33031DE5,
                    0xAA0A4C5F, 0xDD0D7CC9, 0x5005713C, 0x270241AA, 0xBE0B1010,
                    0xC90C2086, 0x5768B525, 0x206F85B3, 0xB966D409, 0xCE61E49F,
                    0x5EDEF90E, 0x29D9C998, 0xB0D09822, 0xC7D7A8B4, 0x59B33D17,
                    0x2EB40D81, 0xB7BD5C3B, 0xC0BA6CAD, 0xEDB88320, 0x9ABFB3B6,
                    0x03B6E20C, 0x74B1D29A, 0xEAD54739, 0x9DD277AF, 0x04DB2615,
                    0x73DC1683, 0xE3630B12, 0x94643B84, 0x0D6D6A3E, 0x7A6A5AA8,
                    0xE40ECF0B, 0x9309FF9D, 0x0A00AE27, 0x7D079EB1, 0xF00F9344,
                    0x8708A3D2, 0x1E01F268, 0x6906C2FE, 0xF762575D, 0x806567CB,
                    0x196C3671, 0x6E6B06E7, 0xFED41B76, 0x89D32BE0, 0x10DA7A5A,
                    0x67DD4ACC, 0xF9B9DF6F, 0x8EBEEFF9, 0x17B7BE43, 0x60B08ED5,
                    0xD6D6A3E8, 0xA1D1937E, 0x38D8C2C4, 0x4FDFF252, 0xD1BB67F1,
                    0xA6BC5767, 0x3FB506DD, 0x48B2364B, 0xD80D2BDA, 0xAF0A1B4C,
                    0x36034AF6, 0x41047A60, 0xDF60EFC3, 0xA867DF55, 0x316E8EEF,
                    0x4669BE79, 0xCB61B38C, 0xBC66831A, 0x256FD2A0, 0x5268E236,
                    0xCC0C7795, 0xBB0B4703, 0x220216B9, 0x5505262F, 0xC5BA3BBE,
                    0xB2BD0B28, 0x2BB45A92, 0x5CB36A04, 0xC2D7FFA7, 0xB5D0CF31,
                    0x2CD99E8B, 0x5BDEAE1D, 0x9B64C2B0, 0xEC63F226, 0x756AA39C,
                    0x026D930A, 0x9C0906A9, 0xEB0E363F, 0x72076785, 0x05005713,
                    0x95BF4A82, 0xE2B87A14, 0x7BB12BAE, 0x0CB61B38, 0x92D28E9B,
                    0xE5D5BE0D, 0x7CDCEFB7, 0x0BDBDF21, 0x86D3D2D4, 0xF1D4E242,
                    0x68DDB3F8, 0x1FDA836E, 0x81BE16CD, 0xF6B9265B, 0x6FB077E1,
                    0x18B74777, 0x88085AE6, 0xFF0F6A70, 0x66063BCA, 0x11010B5C,
                    0x8F659EFF, 0xF862AE69, 0x616BFFD3, 0x166CCF45, 0xA00AE278,
                    0xD70DD2EE, 0x4E048354, 0x3903B3C2, 0xA7672661, 0xD06016F7,
                    0x4969474D, 0x3E6E77DB, 0xAED16A4A, 0xD9D65ADC, 0x40DF0B66,
                    0x37D83BF0, 0xA9BCAE53, 0xDEBB9EC5, 0x47B2CF7F, 0x30B5FFE9,
                    0xBDBDF21C, 0xCABAC28A, 0x53B39330, 0x24B4A3A6, 0xBAD03605,
                    0xCDD70693, 0x54DE5729, 0x23D967BF, 0xB3667A2E, 0xC4614AB8,
                    0x5D681B02, 0x2A6F2B94, 0xB40BBE37, 0xC30C8EA1, 0x5A05DF1B,
                    0x2D02EF8D
                };
        #endregion

        #region CalculateCrc32
        /// <summary>
        /// Calculates the CRC32 of the given bytes.
        /// The CRC32 calculation is similar to the standard one as demonstrated in RFC 1952, 
        /// but with the inversion (before and after the calculation) ommited.
        /// </summary>
        /// <param name="buf">The byte array to calculate CRC32 on </param>
        /// <param name="off">The offset within buf at which the CRC32 calculation will start </param>
        /// <param name="len">The number of bytes on which to calculate the CRC32</param>
        /// <returns>The CRC32 value</returns>
        private static int CalculateCrc32(IList<byte> buf, int off, int len)
        {
            uint c = 0;
            var end = off + len;
            for (var i = off; i < end; i++)
                c = Crc32Table[(c ^ buf[i]) & 0xFF] ^ (c >> 8);
            return (int)c;
        }
        #endregion

        #region GetU32
        /// <summary>
        /// Returns an unsigned 32-bit value from little-endian ordered bytes.
        /// </summary>
        /// <param name="buf">Byte array from which byte values are taken</param>
        /// <param name="offset">Offset the offset within buf from which byte values are taken</param>
        /// <returns>An unsigned 32-bit value as a lon</returns>
        private static long GetU32(IList<byte> buf, int offset)
        {
            return ((buf[offset] & 0xFF) | ((buf[offset + 1] & 0xFF) << 8) | ((buf[offset + 2] & 0xFF) << 16) |
                    ((buf[offset + 3] & 0xFF) << 24)) & 0x00000000FFFFFFFFL;
        }
        #endregion

        #region GetU8
        /// <summary>
        /// Returns an unsigned 8-bit value from a byte array.
        /// </summary>
        /// <param name="buf">A byte array from which byte value is taken</param>
        /// <param name="offset">The offset within buf from which byte value is taken</param>
        /// <returns>An unsigned 8-bit value as an int</returns>
        private static int GetU8(IList<byte> buf, int offset)
        {
            return buf[offset] & 0xFF;
        }
        #endregion

        #region DecompressRtf
        /// <summary>
        /// Decompresses the RTF or throws an IllegalArgumentException if src does 
        /// not contain valid compressed-RTF bytes.
        /// </summary>
        /// <param name="src">Src the compressed-RTF data bytes</param>
        /// <returns>An array containing the decompressed byte</returns>
        public static byte[] DecompressRtf(byte[] src)
        {
            byte[] dst; // destination for uncompressed bytes
            var inPos = 0; // current position in src array
            var outPos = 0; // current position in dst array

            _compressedRtfPrebuf = Encoding.UTF8.GetBytes(Prebuf);

            // get header fields (as defined in RTFLIB.H)
            if (src == null || src.Length < 16)
                throw new Exception("Invalid compressed-RTF header");

            var compressedSize = (int)GetU32(src, inPos);
            inPos += 4;
            var uncompressedSize = (int)GetU32(src, inPos);
            inPos += 4;
            var magic = (int)GetU32(src, inPos);
            inPos += 4;

            if (compressedSize != src.Length - 4) // check size excluding the size field itself
                throw new Exception("compressed-RTF data size mismatch");

            // process the data
            switch (magic)
            {
                case 0x414c454d:
                    dst = new byte[uncompressedSize];
                    Array.Copy(src, inPos, dst, outPos, uncompressedSize- inPos); // just copy it as it is
                    break;

                case 0x75465a4c:
                    {
                        var crc32 = (int)GetU32(src, inPos);
                        inPos += 4;

                        if (crc32 != CalculateCrc32(src, 16, src.Length - 16))
                            throw new Exception("compressed-RTF CRC32 failed");
                        
                        // magic number that identifies the stream as a compressed stream
                        dst = new byte[_compressedRtfPrebuf.Length + uncompressedSize];
                        Array.Copy(_compressedRtfPrebuf, 0, dst, 0, _compressedRtfPrebuf.Length);
                        outPos = _compressedRtfPrebuf.Length;
                        var flagCount = 0;
                        var flags = 0;
                        while (outPos < dst.Length)
                        {
                            // each flag byte flags 8 literals/references, 1 per bit
                            flags = (flagCount++ % 8 == 0) ? GetU8(src, inPos++) : flags >> 1;
                            if ((flags & 1) == 1)
                            { // each flag bit is 1 for reference, 0 for literal
                                var offset = GetU8(src, inPos++);
                                var length = GetU8(src, inPos++);
                                //!!!!!!!!!            offset = (offset << 4) | (length >>> 4); // the offset relative to block start
                                offset = (offset << 4) | (length >> 4); // the offset relative to block start
                                length = (length & 0xF) + 2; // the number of bytes to copy
                                // the decompression buffer is supposed to wrap around back
                                // to the beginning when the end is reached. we save the
                                // need for such a buffer by pointing straight into the data
                                // buffer, and simulating this behaviour by modifying the
                                // pointers appropriately.
                                offset = (outPos / 4096) * 4096 + offset;
                                if (offset >= outPos) // take from previous block
                                    offset -= 4096;
                                // note: can't use System.arraycopy, because the referenced
                                // bytes can cross through the current out position.
                                var end = offset + length;
                                while (offset < end)
                                    dst[outPos++] = dst[offset++];
                            }
                            else
                            { // literal
                                dst[outPos++] = src[inPos++];
                            }
                        }
                        // copy it back without the prebuffered data
                        src = dst;
                        dst = new byte[uncompressedSize];
                        Array.Copy(src, _compressedRtfPrebuf.Length, dst, 0, uncompressedSize);
                    }
                    break;

                default:
                    throw new Exception("Unknown compression type (magic number " + magic + ")");
            }

            return dst;
        }
        #endregion
    }
}
